1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio frequency integrated circuits used in such wireless communication systems.
2. Background of the Invention
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
FIG. 1 is a schematic block diagram of a prior art receiver that may be used as part of the built-in radio transceiver. The receiver includes a low noise amplifier (LNA), mixer stage, band pass filter (BPF), analog to digital converter (ADC), digital channel filter, demodulator, a received signal strength indication (RSSI) module, and an automatic gain control (AGC) module. In operation, the low-noise amplifier (LNA) amplifies a radio frequency signal (RF in) to a level acceptable for processing in subsequent stages of the receiver. The mixer stage, which includes mixers and the variable gain blocks, translates the RF input signal to a low or zero intermediate frequency (IF) signal. The band pass filter filters the low or zero IF signal, which is subsequently converted into a digital low or zero IF signal by the analog-to-digital converter. A digital processor, which performs the digital channel filtering and digital demodulation, recaptures the raw data contained in the received RF signal.
Vital to the operation of the receiver is the accurate and timely setting of the controls of the variable gain blocks, the LNA, and possibly the ADC based on the strength of the received signal. If the gain controls are set inappropriately, the receiver may suffer from reduced sensitivity or may malfunction due to node saturation.
The automatic gain control (AGC) algorithm drives the controls of the variable gain blocks in the receiver to desired settings that allow the receiver to operate optimally. The AGC employs some feedback control law to ensure that the setting of the gain controls occurs in a timely manner. However, proper operation of the AGC algorithm depends upon the availability of an accurate and nearly-instantaneous indication of the strength of the received signal, which is provided by an analog Receiver Signal Strength Indication (RSSI) module.
FIG. 2 is a schematic block diagram of the analog RSSI module, which includes a stage that combines the in-phase and quadrature (I & Q) components of the filtered received signal, a variable gain stage, a rectifier, a band pass filter (BPF), a peak detector, a log-domain uniform quantizer, and some digital control logic.
The rectifier rectifies the received sinusoidal signal, where the rectified sinusoidal signal is subsequently filtered, via the band pass filter, to attenuate noise components and to smooth the rectified signal. The peak detector registers the amplitude of the filtered rectified signal, which is quantized to a desired resolution by a log-domain uniform quantizer to produce a quantizer thermometer output code. The digital logic converts the quantizer thermometer output code to an appropriate digital representation. Since most signal processing in the RSSI blocks is analog, it suffers from relatively high die area requirement, relatively high power consumption, and imprecision due to process and temperature variations.
Therefore, a need exists for a method and apparatus that substantially overcome the relatively high die area, the relatively high power consumption, and the imprecision of analog RSSI modules.